It is quite often that a certain wavelength (optical channel) is required for transmitting different optical signals within a common optical network. This situation causes a physical conflict which needs to be resolved.
The following are some conventional solutions for the situation:                a) Using the wavelength conversion approach (optically or electrically), i.e., changing the channel/wavelength for one of the conflicting optical signals so as to allow passing simultaneously both conflicting signals via a single network node.        b) Rerouting of one of the conflicting optical signals to an alternative route in the network, where it will use the same unchanged wavelength but no conflict with other signals of the same wavelength will occur.        
Still, a problem occurs when the optical channels budget of the network is limited, and/or when two or even more optical signals using the same wavelength/channel are forced to pass via one specific network node/element, and even to be switched in that network node. Another source of the problem may be a huge number of services which should be allocated for the users on a rather limited number of wavelengths. Along with the dramatic increase nowadays of optical traffic being conveyed in optical networks, the problem becomes critical, especially in mesh optical networks where such conflicts are created almost at every node.
There are known methods for multimode optical transmissions, where one and the same optical fiber is adapted to transmit optical signals at two or more different modes, although mode crosstalk between the signals may occur.
For example, some approaches for the multi-mode transmission are described in the following article: R. Ryf et al., “Space-division multiplexing over 10 km of three-mode fiber using coherent 6×6 MIMO processing” (OSA/OFC/NFOEC 2011).
Another approach is described in the article M. Salsi et al. “Transmission at 2×100 Gb/s, over Two Modes of 40 km-long Prototype Few-Mode Fiber, using LCOS-based Mode Multiplexer and Demultiplexer (PDPB9.pdf, OSA/OFC/NFOEC 2011).
G. Stepnyak et al. discloses ways of “Increasing Multimode Fiber Transmission Capacity by Multimode Selective Spatial Light Phase Modulation” ECOC 2010, Paper P6.3 (2010).
Clemens Koebele et al. demonstrate a multi mode division multiplexing system and discuss how data can be transmitted at different modes over a WDM channel, and how the data is affected by cross-talk in a paper “40 km Transmission of Five Mode Division Multiplexed Data Streams at 100 Gb/s at Low MIMO-DSP Complexity” (ECOC Postdeadline Papers© 2011 OSA).
There are also prior art examples, describing multimode optical fiber switching devices.
One example is US 2010/0040325 which describes an all-optical cross connect switch utilizing two-axis MEMS mirrors for cross connecting optical fibers in a first set of optical fibers to optical fibers in a second set of optical fibers. The optical fibers in the first and second sets are precisely positioned in a first fiber-micro lens positioning array to define a first set of parallel collimated cross-connect communication beam paths, wherein each path connects an optical fiber in the first set of optical fibers with a MEMS mirror in a first MEMS mirror array.
Still there is a need to practically and efficiently resolve the problem of switching optical signals being transmitted in various modes via an optical fiber network.